1. Field of the Invention
The present invention relates to a rotating anode X-ray tube a method of manufacturing the rotating anode X-ray tube and, more particularly, to the bearing structure of the rotating anode X-ray tube.
2. Description of the Related Art
As is well known, in a rotating anode X-ray tube, a disk-like anode target is supported by rotary and stationary structures having bearing portions. The electromagnetic coil of a stator disposed outside the vacuum envelope is energized to rotate the rotary structure fixed on the anode target at a high speed. The electron beam emitted from a cathode bombards the surface of the anode target, so that the anode target irradiates X-rays. Each bearing portion is constituted by a roller bearing, e.g., a ball bearing, or a dynamic pressure type slide bearing having a bearing surface formed with helical grooves and a liquid metal lubricant, e.g., Ga or a gallium--indium--tin (Ga--In--Sn) alloy, filling the gap between the bearings. Rotating anode X-ray tubes using the latter slide bearings are disclosed in, e.g., Published Examined Japanese Patent Application No. 60-21463 and Published Unexamined Japanese Patent Application Nos. 60-97536, 60-117531, 62-287555, and 2-227948.
In each of the rotating anode X-ray tubes disclosed in the above gazettes, the bearing gap between the bearing surface facing the dynamic pressure type slide bearing, having helical grooves is about, e.g., 20 .mu.m, and a liquid metal lubricant is applied in the helical grooves and the bearing gap. When the amount of the lubricant is excessively small, the slide bearing cannot obtain a sufficiently high dynamic pressure, as a matter of course, and the dynamic pressure type slide bearing cannot maintain a stable operation. On the other hand, when the amount of lubricant is excessively large, the lubricant tends to leak to the outside of the bearing portion. The leak occurs, when gas emission occurs from the bearing constituent member, from the lubricant during assembly or from actual operation of the X-ray tube, due to part of the lubricant being blown off to the outside from the bearing portion together with gas bubbles. When this phenomenon occurs, the stable dynamic pressure bearing operation of the slide bearing cannot be obtained, and the liquid metal lubricant scattered in the X-ray tube envelope considerably damages the breakdown voltage performance.